Effective Span of Stairs

1. When the flight of the stair is supported at the ends of landing beams, the effective span is taken as the projected horizontal distance between the centre lines of landing beam.
2. When the stairs are not provided with stringer beam, then the effective span shall be taken as the following horizontal distances:(i) Where supported at top and bottom risers by beams standing parallel with the risers, the distance centre-to-centre of beams.(ii) Where spanning on to the edge of a landing slab, which spans parallel with the risers (Fig. 21.15) a distance equal to the going of the stairs plus at each one, either half the width of landing or 1 m, whichever is smaller.(iii) Where the landing slab spans in the same direction as the stairs, they shall be considered as acting together to form a single slab and the span is determined as the distance centre-to-centre of the supporting beam or walls, the going being measured horizontally.

Figure 21.15 Effective span for stairs supported at each end by landings (Source: IS: 456–2000)